The hemostatic balance is regulated by vascular bed-specific endothelial cell signaling pathways. We propose that coronary artery thrombosis arises through local alterations in one or more of these pathways. The overall goals of the Collaborative Program are to elucidate the molecular basis of endothelial cell subtype-specific gene expression in the heart and to identify the critical components of cardiac hemostasis. Specific Aim 1) Dr. Rosenberg will study the role of a platelet-derived growth factor signaling pathway in mediating expression of a gene program within cardiac microvascular endothelial cells that includes tissue factor (TF). He will also optimize a recently developed mouse model of coronary artery thrombosis. Specific Aim 2) Dr. Aird will examine the role of the Egr-1 transcription factor in mediating cardiac-specific hemostasis. He will ask how a single gene can serve to "fine tune" hemostasis according to the local needs of the tissue. Specific Aim 3) Dr. Mackman will evaluate the role of a thrombin-PAR-1 signaling pathway in governing local levels of pro-coagulant (TF) and fibrinolytic (tissue-type plasminogen activator) molecules within the heart. In addition, he will address the contribution of monocyte-plasminogen activator) molecules within the heart. In addition, he will address the contribution of monocyte-derived TF to cardiac hemostasis. Specific Aim 4) Dr. Housman will use genetic approaches in large populations to identify genotypes which significantly contribute to coronary thrombosis. The three basic science projects Specific Aims 1-3) are interrelated by several common themes. Each component involves: (1) the study of a cardiac endothelial cell type-specific signaling pathway, (2) the determination of the effects of cell type-specific signaling pathways on global hemostasis (fibrin deposition), (3) the study of TF gene regulation and its role as the initiator of coagulation in the cardiac circulation, and (4) the use of transgenic mouse technology for studying vascular-bed specific hemostasis in the heart. The clinical project will serve as a vital link to validate the role of local hemostatic components in human populations. Dr. Rosenberg provides expertise in both genetic mouse models of hypercoagulability and in the functional analysis of in vivo hemostasis. Dr. Aird contributes tools for studying vascular gene-specific gene regulation. Dr. Mackman has experience in studying TF gene regulation in cultured cells and animal models. Dr. Housman is an acknowledged expert in human genomics. Taken together, the individual projects and the collaborative efforts promise to provide important insight into the molecular basis of cardiac hemostasis.